1. Field of the Invention
The present invention generally relates to a packet-based generating method, and more particularly to a generating method for Short Training Field (STF) useful to IEEE 802.11n Wireless Local Area Network (WLAN) communication system.
2. Background Art
In a wireless communication system, the packet format normally includes a fixed-pattern preamble. The preamble serves several purposes, namely, to identify the packet type, and to provide signal for Direct Current (DC) offset estimation, frequency offset estimation and channel estimation. In most wireless communication systems, an important field of the preamble is High-Throughput Short Training Field (HT-STF).
The IEEE 802.11n draft specification [1] specifies four bandwidth (BW) configurations. The first one is a simple 20 MHz BW. The second configuration is 40 MHz BW. The third configuration is that a transmitter nominally operating in the 40 MHz BW mode may use the lower 20 MHz BW only to transmit. The fourth configuration is that a transmitter nominally operating in the 40 MHz BW mode may use the upper 20 MHz only to transmit. The HT-STF in each of these four configurations is mathematically derived from a different frequency-domain sequence, but the transmitter needs to transmit the corresponding time-domain sequence. A transmitter could store these frequency-domain sequences in the Read-Only Memory (ROM) and performs a Fast Fourier Transform (FFT) operation before transmitting the time-domain sequence. But a more efficient way is to store the time-domain sequence in the ROM. In this case, it is required to store all four sets of time-domain HT-STF sequences. Since there are 64 or 128 complex samples (real and imaginary parts) in HT-STF for each mode and a number of bits are required for each real or imaginary sample, the total buffer size becomes significant. If over-sampling is implemented at transmitter, the required buffer size will be further multiplied.
Several U.S. Patent Applications including: U.S. Patent Application 20060274852, entitled as “Modified preamble for programmable transmitter”, Dec. 7, 2006; U.S. Patent Application 20060274847, entitled as “Training frames for MIMO stations”, Dec. 7, 2006; U.S. Patent Application 20060193340, entitled as “Wireless messaging preambles allowing for beamforming and legacy device coexistence”, Aug. 31, 2006; U.S. Patent Application 20060088120, entitled as “Mixed mode preamble for MIMO wireless communications”, Apr. 27, 2006; U.S. Patent Application 20050286474, entitled as “Modified preamble structure for IEEE 802.11a extensions to allow for coexistence and interoperability between 802.11a devices and higher data rate, MIMO or otherwise extended devices”, Dec. 29, 2005; U.S. Patent Application 20050233709, entitled as “Modified preamble structure for IEEE 802.11a extensions to allow for coexistence and interoperability between 802.11a devices and higher data rate, MIMO or otherwise extended devices”, Oct. 20, 2005; U.S. Patent Application 20050180360, entitled as “Preamble formats for MIMO wireless communications”, Aug. 18, 2005; U.S. Patent Application 20050113026, entitled as “Frame format for high data throughput wireless local area network transmissions”, May 26, 2005; and U.S. Patent Application 20050180368, “Multiple protocol wireless communications in a WLAN”, Aug. 18, 2005; are prior arts claiming the format of HT-STF, and their intents are to become the essential patent for implementing IEEE 802.11n draft specification. However, none of these prior arts mentioned any methods of efficient generating method with reduced ROM requirement and simple arithmetic operations to generate all the time-domain HT-STF sequences for all four BW configurations.